Caution: invalid backup GPT Header (gdisk)

Question

Each time I boot into my Ubuntu installation, when I open gdisk I am given the messages:

GPT fdisk (gdisk) version 0.8.8

Type device filename, or press <Enter> to exit: /dev/sda
Caution: invalid backup GPT header, but valid main header; regenerating
backup header from main header.

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: damaged

****************************************************************************
Caution: Found protective or hybrid MBR and corrupt GPT. Using GPT, but disk
verification and recovery are STRONGLY recommended.
****************************************************************************

If I just hit w and write the table, then rerunning gdisk without a reboot will open without complaint.

GPT fdisk (gdisk) version 0.8.8

Type device filename, or press <Enter> to exit: /dev/sda
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

However, when I restart, I'm back to an "invalid backup GPT header". My Ubuntu installation boots just fine using rEFInd, as does my LFS installation. My Win7 installation seems to be currently lost although I'm hoping that will be easily fixed once I get some suitable recovery USB pen/disk etc set up.

What's causing this "invalid backup GPT header"? Should I be worried?

Answer 1

I had the same problem. Eventually I tracked it down to the firmware overwriting the CRC entries in the backup GPT header every boot to some invalid value. Change the disk mode in the firmware setup from RAID to AHCI stopped it from doing this (and I wasn't using RAID anyway).